FACTORS AFFECTING SERUM SELENIUM AND VITAMIN-E CONCENTRATIONS IN DAIRY-COWS

Supplementation of selenium and vitamin E to enhance disease resistanc e in dairy cattle has become common, particularly to prevent peripartu rient reproductive disorders and mastitis. To establish reference valu es for serum vitamin E and selenium concentrations in postparturient d airy cattle and to determine whether serum concentrations of these mic ronutrients varied with season and stage of lactation, cows from a str atified random sample of 50 herds were studied for 1 year. Blood sampl es were collected from each of the 50 study herds twice, from the 10 m ost recently parturient cows or from 10% of the herd, whichever was gr eatest. Mean concentration of vitamin E and selenium was 2.55 mu g/ml and 78.12 ng/ml, respectively. Vitamin E concentrations were significa ntly (P < 0.05) higher during the summer and Jail than during the wint er and spring. Selenium concentrations were significantly (P < 0.05) l ower during the summer and Jail than during the winter and spring. Her d, season of blood sample collection, and time since parturition were significant (P < 0.02) in explaining variation in vitamin E and seleni um concentrations.